This invention relates to a novel poly(vinyl)phenol polymers partially silylated at the phenolic hydroxyl and to methods for making such polymers and using such polymers in the fabrication of devices used in the electronics industry and in particular to fabrication utilizing lithographic processes.
Photolithography is a commonly used technique in transposing a pattern to a base, which utilizes a radiation-sensitive polymer generally referred to as photoresist. In photolithography the resist material is applied as a thin coating over some base and subsequently exposed in an image-wise fashion (through a mask) such that radiation, e.g., U.V. or visible light, x-rays, electron beam, strikes selected areas of the resist material. The exposed resist is then subjected to a development step. Depending upon the chemical nature of the resist material, the exposed areas may be rendered more soluble in some developing solvents than the unexposed areas, thereby producing a positive tone image of the mask. Conversely, the exposed areas may be rendered less souble producing a negative tone image of the mask. The net effect of this process is to produce a three dimensional relief image in the resist material that is a replication of the opaque and transparent areas on the mask.
The areas of resist that remain following the imaging and developing processes are used to mask the underlying substrate for subsequent etching or other image transfer steps. If, for example, the underlying substrate or base were SiO.sub.2, immersion of the structure into an etchant such as buffered hydrofluoric acid ("wet etching") or in an organo-halide plasma or other reactive ion etching ("RIE") medium, would result in selective etching of the SiO.sub.2 in those areas that were bared during the development step. The resist material "resists" the etchant and prevents it from attacking the underlying substrate in those areas where it remains in place after development. After the exposed material has been removed by plasma or wet chemical etching, the photoresist mask is then taken off.
Photoresists are used in the fabrication of semiconductors. The photoresist is coated onto the surface of a semiconductor wafer and then imaged and developed. Following development, the wafer is typically etched with an etchant whereby the portions of the wafer exposed by development of the photoresist are dissolved while the portions of the wafer coated with photoresist are protected, thereby defining a circuit pattern.
The positive-working resists comprise a radiation sensitive compound in a film-forming polymer binder. The radiation sensitive compounds, or sensitizers as they are often called, most frequently used where the radiation is light are esters and amides formed from o-quinone diazide sulfonic and carboxylic acids. These esters and amides are well known in the art and are described by DeForest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, pages 47-55 (1975), incorporated herein by reference. These light sensitive compounds, and the methods used to make the same, are all well documented in prior patents including German Pat. No. 865,140 granted Feb. 2, 1953 and U.S. Pat. Nos. 2,767,092; 3,046,110; 3,046,112; 3,046,119; 3,046,121; 3,046,122 and 3,106,465, all incorporated herein by reference. Additional sulfonic amide sensitizers that have been used in the formulation of positive-acting photoresists are shown in U.S. Pat. No. 3,637,384, also incorporated herein by reference. These materials are formed by the reaction of a suitable diazide of an aromatic sulfonyl chloride with an appropriate resin amine. Methods for the manufacture of these sensitizers and examples of the same are shown in U.S. Pat. No. 2,797,213 incorporated herein by reference. Other positive-working diazo compounds have been used for specific purposes. For example, a diazo compound used as a positive-working photoresist for deep U.V. lithography is Meldrum's diazo and its analogs as described by Clecak, et al., Technical Disclosure Bulletin, Volume 24, Number 4, September 1981, IBM Corporation, pp 1907 and 1908. An o-quinone diazide compound suitable for laser imaging is shown in U.S. Pat. No. 4,207,107. The aforesaid references are also incorporated herein by reference.
A class of negative resists comprising a negative acting sensitizer in a polymer binder is described by Iwayanagi, et al., IEEE Transactions on Electron Devices, Vol. ED-28, No. 11, November, 1981, incorporated herein by reference. The resists of this reference comprise an aromatic azide in a phenolic binder. It is believed that these resists are first disclosed and claimed in U.S. Pat. No. 3,869,292, also incorporated herein by reference. Additional aromatic azide sensitizers are disclosed by DeForest, supra, and U.S. Pat. Nos. 2,940,853 and 2,852,379, incorporated herein by reference. The most familiar negative photoresists are two-component, resist materials which consist of a cyclized synthetic rubber matrix resin which is radiation insensitive but forms excellent films. This resin is combined with a bis-arylazide sensitizer.
Photoresist compositions are well known in the art and are described in numerous publications including DeForest, supra; Introduction to Microlithography, supra, Chap. 3, Willson, C. G. Silicon containing polymers have been widely studied as components of photoresists used in processes involving oxygen-RIE pattern transfer. Such polymers typically have high oxygen-RIE sensitivity. In general, the etch rate of organosilicon polymers in an oxygen plasma is dependent only on the silicon content. See, e.g., Materials for Microlithography, Thompson, L. F., et al., eds., A.C.S. Symposium Series 266, Chap. 15, 1984.
One class of uv sensitive, oxygen RIE resistant silicon containing polymers used in bilayer processes is the polysiloxanes (See, e.g., Hatzakis, M. J., J. Vac. Sci. Technol., 26 (1979) 2984). These polymers can function both as negative resists and oxygen RIE barriers.
Other silicon containing polymers for use in photoresists are known in the art. For example, Saotome, Y., et al., J. Electro Chem. Soc.: Solid-State Sci. and Tech., 132 (1985) 909, disclose a silicon containing polymer for use in a positive photoresist as the thin top or resolution layer in a bi-layer resist system. This photoresist, a partly trimethylsilylmethylated resorcinol-formaldehyde resin mixed with a naphthoquinonediazide, was thinly coated onto a thick layer of polyimide resin on a silicon wafer.
Kawazu, R., et al., J. Vac. Sci. Technol. B4(1) (January/February 1986) 409, disclosed silyl ethers of novolak and low molecular weight resist for use in tri-level and bi-level resist systems. U.S. Pat. No. 4,564,576 teaches a polymer having allyl groups each attached to a silicon atom as a resist material.
Essentially 100% silylated poly(vinyl)phenol polymers for use in a positive optical resist for bilayer resist systems were disclosed by Buiguez, F., et al. at the Micro Circuits Engineering Conference in Berlin in 1984 by a Poster Paper presented on behalf of Commissariat a l'Energie Atomique, France. See also EPO No. 0 178208. The polymers used in making these resists are produced by first silylating vinyl phenol and then polymerizing the silylated phenol by a free radical polymerization process. The resists contain at least one salt capable of being converted into a Brunsted acid upon appropriate irradiation and one photosensitizer. According to these workers, the resist can be developed and the substrate simultaneously etched by dry processing with a gaseous plasma.
Silicon containing polymers known in the art for use in making electronic devices suffer from various disadvantages such as, for example, development requiring organic solvents, complicated procedures for synthesizing the polymers, halogen and other metal ion contamination. Thus, new silicon containing polymers are being sought, in particular, for use in the fabrication of devices in the electronics industry.